13,527 research outputs found
Some fundamental problems for an energy conserving adaptive resolution molecular dynamics scheme
Adaptive resolution molecular dynamics (MD) schemes allow for changing the
number of degrees of freedom on the fly and preserve the free exchange of
particles between regions of different resolution. There are two main
alternatives on how to design the algorithm to switch resolution using
auxiliary ''switching'' functions; force based and potential energy based
approach. In this work we show that, in the framework of classical MD, the
latter presents fundamental conceptual problems which make unlikely, if not
impossible, the derivation of a robust algorithm based on the potential energy.Comment: 4 pages, 1 figure (color); Phys.Rev.E (2007) in pres
Shannon Entropy and Many-Electron Correlations: Theoretical Concepts, Numerical Results and Collins Conjecture
In this paper I will discuss the overlap between the concept of Shannon
Entropy and the concept of electronic correlation. Quantum Monte Carlo
numerical results for the uniform electron gas are also presented; these latter
on the one hand enhance the hypothesis of a direct link between the two
concepts but on the other hand leave a series of open questions which may be
employed to trace a roadmap for the future research in the field.Comment: 27 pages with 3 figure
Levy-Lieb principle: The bridge between the electron density of Density Functional Theory and the wavefunction of Quantum Monte Carlo
The constrained-search principle introduced by Levy and Lieb, is proposed as
a practical, though conceptually rigorous, link between Density Functional
Theory (DFT) and Quantum Monte Carlo (QMC). The resulting numerical protocol
realizes in practice the implicit key statement of DFT: "Given the three
dimensional electron density of the ground state of a system of N electrons
with external potential v(r) it is possible to find the corresponding
3N-dimensional wavefunction of ground state." From a numerical point of view,
the proposed protocol can be employed to speed up the QMC procedure by
employing DFT densities as a pre-selection criterion for the sampling of
wavefunctions.Comment: 9 pages, 1 figure, paper in press in Chemical Physics Letters, 201
Bader's interatomic surface and Bohmian mechanics
A Thomas-Fermi statistical analysis of Bader's interatomic surface developed
in a previous work (L.Delle Site, Phys.Lett.A 286 61-64 (2001)) is here
extended by considering exchange effects and electron density's inhomogeneity
at basic level via Thomas-Fermi-Dirac-Weizsacker model. The results obtained
show interesting connections with bohmian mechanics and lead to a statistical
interpretation of the chemical properties of condensed systems at atomistic
level.Comment: 8 pages, no figure
Grand-Canonical Adaptive Resolution Centroid Molecular Dynamics: Implementation and Application
We have implemented the Centroid Molecular Dynamics scheme (CMD) into the
Grand Canonical-like version of the Adaptive Resolution Simulation Molecular
Dynamics (GC-AdResS) method. We have tested the implementation on two different
systems, liquid parahydrogen at extreme thermodynamic conditions and liquid
water at ambient conditions; the reproduction of structural as well as
dynamical results of reference systems are highly satisfactory. The capability
of performing GC-AdResS CMD simulations allows for the treatment of a system
characterized by some quantum features and open boundaries. This latter
characteristic not only is of computational convenience, allowing for
equivalent results of much larger and computationally more expensive systems,
but also suggests a tool of analysis so far not explored, that is the
unambiguous identification of the essential (quantum) degrees of freedom
required for a given property
Monetary policy and potential output uncertainty: a quantitative assessment
I estimate a dynamic stochastic general equilibrium model where the policymaker and the private sector have imperfect knowledge about potential output. The estimation of the structural parameters and of the monetary authorities’objectives is key to assess the quantitative relevance of the imperfect information problem and to evaluate the robustness of previous exercises based on calibration. The estimated model also allows me to revisit the Orphanides (2001, 2003) findings that the central bank can makes large and persistent mistakes to estimate potential output in response to productivity and cost shocks. I find that when real unit labor cost is used as a monetary policy indicator, the potential output uncertainty has quantitatively negligible consequences on policy behaviour and inflation dynamics. JEL Classification: E4, E5indicator variables, monetary policy, potential output uncertainty, real unit labor cost
Solvation of positive ions in water: The dominant role of water-water interaction
Local polarization effects, induced by mono and divalent positive ions in
water, influence (and in turn are influenced by) the large scale structural
properties of the solvent. Experiments can only distinguish this process of
interplay in a generic qualitative way. Instead, first principles quantum
calculations can address the question at both electronic and atomistic scale,
accounting for electronic polarization as well as geometrical conformations.
For this reason we study the extension of the scales' interconnection by means
of first principle Car-Parrinello molecular dynamics applied to systems of
different size. In this way we identify the general aspects dominating the
physics of the first solvation shell and their connection to the effects
related to the formation of the outer shells and eventually the bulk. We show
that while the influence of the ions is extended to the first shell only, the
water-water interaction is instead playing a dominant role even within the
first shell independently from the size or the charge of the ion.Comment: 4 pages 3 figures (color
Massless Scalar Degrees of Freedom in QCD and in the Electroweak Sector from the Trace Anomaly
The interaction of QCD and electroweak sector with gravity is characterized
by the generation of a massless pole in a specific form factor present in the
1-loop effective action. We briefly illustrate how to single out this behaviour
in perturbation theory, by taking as an example the vertex, with
denoting the energy momentum tensor of the Standard Model. The breaking of
scale invariance, due to the trace anomaly, is then related to the appearance
of a local degree of freedom in the effective action, which is of dilaton type.Comment: 5 pages, presented at the workshop "QCD@work", Lecce, June 18-21,
201
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